Amplifier circuits



I March 26, 1940. F. H. SHEPARD, JR

AMPLIFIER CIRCUITS Original Filed May 28, 1934 OUTPUT 0.6.

0 A gnu 4 INVENTOR FRANCIS .SH PARDJR. BY

ATTORNEY Patented Mar. 26, 1940 t I UNITED T TES-" ATENT OFFICE AMPLIFIER CIRCUITS Francis H. Shepard, Jr., Rutherford, N J.,assigner to Radio Corporation of America, a corporation of Delaware Original application May 28, 1934, Serial No. 727,968. Divided and this application June 10,

1938, Serial No. 212,895

' dClaims. (01.179-171) This applicationis a'division of my copending ply system through terminals l and 2. For purapplication Serial No. 727,968, filed May 28, 1934, poses of. illustration only three tubes. T5, T6 and now U. S. Patent No. 2,137,419, issued November T7 have been shown comprising the amplifier, 22, 1938. however, it is to be distinctly understood that 5 The present invention relates generally to amany desired number of tubes may be utilized and 5 plifiers and more particularly to so called D. C. connected as taught by the present disclosure. amplifiers of the typeadapted to amplify D. C. The first tube T5 includes anode. cathode and and low frequency A. C.- I grid electrodes. Qne side of the cathode is con- For many applications it is desirable to have neeted to line 6 while the anode is connected to l an amplifier that will efiiciently amplify small conductor through condenser C8. The anode is W D. C. voltages. In systems heretofore known, also connected to conductor 6 through two paths Where more than one stage of amplification is one of which includes the resistor R10 and the needed, D. C. amplification is not obtained easily other a resistor. R11 and a condenser C9 in series. for the reasons that either there must be sepa- The D. C. input is applied across terminals 3 15 rate batteries for each stage, or a set of buck- ,and 4, terminal 3 being connected to the grid ing batteries for each stage, or a set of, divider of T5 while terminal 4 is connected to a point on resistors for each stage, or again, a very high the resistor R10 by means of a variable tap 12. voltage source across which the various stages A condenser C1 is connected between the conmay be placed in series with each other, or a nection from terminal 4 to the resistor R10 and g modulator system where the D. C. is converted conductor 6. l into A. C.,-amplified and then re-converted back The second tube is also shown as including into D. C. All of the methods mentioned above anode, cathode and grid electrodes, the anode are more or less complicated and furthermore being connected to the conductor 5 through a are quite critical to adjust. It is also desirable condenser C10 while one side of the cathode is 35 to have an amplifier operating directly on raw connected directly to the conductor 6. The sig- A. C. for use with a photo tube and other indusnal grid of the tube T6 is connected to a point trial uses as, for instance, temperature control on the resistor R11 bymeans of a variable tap l3. systems and burglar alarm systems. As in the case of tube T5 the anode of tube T6 The present invention may be broadly stated is connected to the conductor 6 through twov to comprise a method and means for cascading paths. One of these paths includes a resistor 30 grid controlled rectifiers to produce a D. C. am- R12 while the other comprises resistor R13 and a plifier system which does not necessitate cascadcondenser C11 in series. The third tube of the ing the necessary tube energizing voltages. The system T7 is also provided with anode, cathode invention also contemplates a method and means and grid electrodes, the cathode being connected for correcting for variations in the supply voltdirectly to the conductor 6 while the grid elec- :13

- age. trode is connected to a point intermediate re- Broadly speaking, in the present system the sistor l3 and condenser C11. The anode of tube negativevoltage developed on the plate of a grid T7 is connected to an output terminal ll, termicontrolled rectifier tube connected across an A. C. nal Ill shown at one end of the conductor 5 be- 40 line is used to bias the grid of a following tube ing the other output terminal of the system. 'It to also connected across the line. The energy to is to be understood that any desired utilizing sysbe amplified is impressed across the input of the tem may be connected across the output termifirst tube and the amplified energy is available nals l0 and H." 1

across the output of the last tube. For a proper 'understanding of the operation 5 The invention will be more readily understood of the system shown in the drawing, attention from the following detailed description thereof is directed to the curve sheets shown in Figures and byreference to the drawing, the single figure 1 and 2 of my parentv application. It will be of which shows a preferred embodiment of the noted that the load line OC starts from zero as invention. there is no D. C. supply in the circuit shown in The drawing shows in diagrammatic form a the present application. The plate voltage will 50 simplified A. C. operated D. C. amplifier circuit always be negative as shown by the intersections that is self biased and compensated for line volt- With the triode rectification curves. The actual age variations. As in Figures 5 through 8 of my value of D. C3. plate voltage with aconstant A. C. parent application conductors 5 and 6 of the voltage onthe plate will vary with the grid bias.

present case are connected to an A. C. power sup- This is shown by observing the intersections of 55 the constant A. C. lines with the D. C. load line in Figures 1 and 2 of the parent case.

In normal operation, considering the tube T5, the anode will assume a highly negative average D. C. potential due to the rectifying action of the tube. This potential, for best amplification, will be too high a value to use directly for self-bias. However, since the load resistor is returned to ground or zero potential, a slider may be placed on this resistor to obtain any average D. C. voltage from zero to the average D, C. potential .of the plate. It is possible in some particular instance that the D. C. potential may be in the order of --80 volts.

If -l volts is the normal bias for the tube in this circuit, the slider is adjusted along the load resistor R10 until a potential of w 4 volts is reached. Condenser C7 is used as a filter to bypass the A. C. on the top portion of the divider resistor R10. This will keep the A. '0. off the grid of the tube T5. If. the normal bias is 4 volts, when the plate potential is 80 volts, the slider will be set approximately 1/20 of the way up the loadresistor R10 and the degeneration due to the self-bias will be one part in 20, times the actual realized voltage gain. It should be understood, of course, that the values given above are approximate values that can be expected in normal operation of the system.

The potentiometer R11 as far as D, C. is concerned is merely a. resistor, of negligible value in series with the grid of tube T6. Condensers C10 and C11 have no elTect on the D. C. voltage, however, potentiometer Rh as far as A. C. is conv filament voltage variations.

cerned will act as a voltage divider resistor across the line. impedance to A. C. The instantaneous potential on the grid of tube T6 is the sum of the D. C. voltage on the plate of tube T5 and the instantaneous value of A. C. at the point to which the slider I3 is set on the resistor R11. Duringthe part of the cycle that the tube T6 is conducting the instantaneous A, C. voltage applied to the grid of tube T6 is in such a direction as to oppose the normal D. C. bias supplied by the plate of the vacuum tube T5.

Thus, the grid during the conducting part of the cycle will be less negative than the normal bias and will be of such a value thatthe grid of the tube Ts will be at a suitable operating potential.

Suppose that the A. C. line voltage, that is, the A. C. voltage on the anode is increased it can be seen from the rectification curves in Figures 1 and 2 that the negative plate potential will increase. This will cause the normal grid bias of tube T6 to become more negative. However, increasing the A. C. line voltage would also cause an increase in the superimposed A. C, on the grid on the tube T6 and this will tend to make the grid more positive during'the operating part of the cycle. Since the two above mentioned effects can be made to oppose each other the effects of line voltage variations may benullified. Compensation adjustment is made by varying the A. C. voltage on the grid of tube Ts by adjusting the slider l3 on the. potentiometer R11. As previously stated, it is possible to obtain over compensation, hence, it is possible to perform all the necessary compensation for several stages in the one stage. It is also possible as previously pointed out to accomplish compensation for the effects of The explanationfo-r filament compensation in the circuit is similar to that given in the parent application inconnec- Condensers Ca and C9 have negligible tion with the description of curve sheet shown in Figure 4 thereof.

In the system shown in the present case the slider l3 should be adjusted along the resistor Ru so that the grid of the tube Ts swings into the operating range of the tube but never swings positive with respect to the cathode.

In practice it has been .found that the values of none of the resistances and condensers used are critical. In one of a number of practical embodiments of" the invention, and in particular one that followed the diagram shown in Fig. 8 of the parent case a 2000 ohms resistor was used for the A. C, line shunt while the plate resistances were *each one megohm, the grid resistors two megohr'ns I and the condensers 0.l mmf.

1. In a direct current energy amplifier, an,

electronic rectifier tube provided: with an anode,

a cathode and a control electrOde apair of line conductors. adapted .to be connected to a source I .ofalternating current, means including a cone denser for connecting the anode of said tube to. one of said line conductors, a pair of parallel paths for connecting the anode to-the other line conductor, one of said paths including a resistor element, the other thereof including a resistor ele-,,,

ment and a condenser in series, a connection between said other conductor and the cathode of the tube, an input circuit for said tube including a pair of terminals for connecting the input circuit to a source of energy to be amplified, one of said terminals being connected to'the grid of the tube while the other thereof is variably disposed on.

the first named resistor element,- a condenser shunted between the; connection from the last named terminal to the resistor element and said other conductor, second electronic tube pro vided with anode, cathode, and grid electrodes,

a connection from the anode of said second tube to said other conductor including a resistor element, means for variably connecting the grid of said second tube to a point on said second named resistor element, means including a reactance device for connecting the anode of said second 1 tube to the first named conductor and a connection from the cathode; of the second tube to the other line conductor, said second tube having including an anode and a cathode adapted to be' connected respectively to opposite conductors of an alternating current power supply line to thereby impress alternating current voltage be-'' tween the anode and cathode oi'the discharge tube, a control grid for said tube, a path conductive to direct current and including a resistor connected between the anode and cathode of said tube, an alternating current path including a resistor and a condenser in series, connected in parallel with said first named resistor, a'pair of input terminals for said amplifier, one of said input'terminals being connected to said control.

grid, the other thereof being connected to an intermediate. point or" the first .namedresistor,

and a utilizing circuit connected between a point of the second named resistor and said cathode.

3. An arrangement as described in the next preceding claim characterized by that the utilizing circuit comprises a second space discharge device having an anode and a cathode connected respectivelyto the opposite conductors of the electrical power supply'line, and a grid electrode connected to a point of the resistor of the alternating current circuit.

1. In a relay circuit, a pair of line conductors adapted to be connected to an alternating current network, a first electronic tube having an anode, a cathode and a grid electrode, a connection including a condenser between the anode and one of said line conductors, means connecting the cathode to the other line conductor, a resistor connected between the anode and the last named line conductor, a second connection between the anode and said last named line conductor including a resistor and a condenser in series, a pair of input terminals one thereof being connected to the grid electrode and the I other to the point of the first namedresistor, a

named line conductor and a grid electrode connected to a point of the second named resistor, means for connecting the last named anode to the second named line conductor including a resistor, a second connection between the last named anode and said second named line conductor including a resistor and a condenser in series, a third electronic tube includingv an anode, a cathode and a grid electrode, a pair of output terminals, means for connecting one of said output terminals to said first named line conductor and the other output terminal to the last named anode, means for connecting the last named cathode to the second named line conductor and a connection between the grid ofv said third electronic tube and a-point of the last named resistor. FRANCIS H. SHEPARD, JR. 

